Darpa to fund optical interconnect research

PORTLAND, Ore.  IBM Corp. will team with Agilent Technologies to pursue fabled "terabit per second optical interconnect" technology for multiprocessing servers under a four-year, $30 million effort backed by the Defense Advanced Research Projects Agency (Darpa).

The effort aims to build chip-sized modules that interconnect high-speed microprocessors at aggregated data rates of up to a terabit per second.

"We are looking beyond cabled rack-to-rack technology to very high levels of integration and to do that we need [optical] modules about two centimeters square right on the board next to the microprocessor. We will increase per-channel speed, but probably our most aggressive goal is to reduce power to 5-to-10 milliwatts per gigabit," said Marc Taubenblatt, senior manager of optical communications at IBM Research.

"The main goal of this program is to reach terabit-per-second speeds in a form factor small enough to enable chip-to-chip interconnects," said Waguih Ishak, director of the Communications and Optics Research Laboratory at Agilent. "This will only be achieved by developing
miniature optical components, pushing their operating speeds to 40 gigabits per second (Gbps) and higher, and by clever integration and packaging techniques."

By combining many separate channels into modules, the team hopes to aggregate data rates up to 1 terabit per second per module, with each high-speed channel optimized for dramatically less cost and power consumption that discrete components utilize today (up to 15 Gbps for parallel links, and up to 40 Gbps for components).

By integrating the modules directly on the board with the
microprocessors much higher levels of integration (microprocessors per cubic foot) will utilize very short runs of electrical lines to optical modules that interconnect the computer chips with optical transceivers and waveguides.
The team's basic technology for optical interconnects will be to use vertical-cavity surface-emitting laser (VCSEL) diode arrays to transmit and conventional photo diodes and waveguides to receive (and free-space optics for interconnect paths).

The benefits of optical interconnects are only enjoyed by
communications between large computer systems, but 2mm2 optical modules will transfer the technology inside the box. IBM estimates that the total communications bandwidth inside servers will continue to increase 10-fold every four years, thereby increasing the number of
processors per system until 2010, when IBM predicts a bandwidth of about 40 terabits per second (Tbps) will be needed between
microprocessors.

IBM and Agilent's long-term goal is to develop optical-interconnect technology that delivers 40-terabit performance by 2010 and in a low-power, low-cost, high-density form factor. For instance, DARPA's High Productivity Computing Systems (HPCS) initiative will require these kinds of on-board speeds for future military multiprocessors.

(IBM is already participating in DARPA's HPCS project by creating what it calls PERCS for Productive, Easy-to-use, Reliable Computing System.)

IBM Research claims to be the world's largest information technology research organization, housing over 3,000 scientists and engineers in eight labs in six countries.

Agilent Laboratories was formerly part of Hewlett-Packard Laboratories, but now employs over 300 researchers and support staff in Palo Alto, Calif.